First, cheapest and probably most effective thing to do with a deluxe reverb is to remove the bright cap from the normal channel. Although the reissues are not as easy to work on as the old ones due to their construction, it is still a super easy and reversible mod. In about 90% of cases that will take away the spike you are hearing. When the amp is cranked to full, the bright cap essentially does nothing, but at lower volumes its effect is more pronounced as everything above a certain frequency is being amplified as if the amp was fully cranked. If you remove the bright cap, your amp will amplify all frequencies more evenly across the volume range. I would do this first before swapping any tubes. Some of the bigger fenders like supers and twins have the bright circuit with a switch, given that deluxes don't have a switch, you might find that simply removing the cap will give you exactly what you want and you will never hear an annoying spike again.
Second thing you can look at which doesn't require any mods (apart from undoing a few bolts), but costs a bit more is speaker swapping.
What speaker did it come with?
If it is the Jensen c12k, changing that out will do more than anything to modify you tone in a meaningful way. Far more than any tube swaps. I have never though that deluxes or any blackface style fender have a "mid spike" quite the opposite in fact, but many of them have a definite "spike" up in the high frequencies, partly this is the bright circuit, but also the speakers natural eq contributes too. Those jensen speakers have it in spades and you cant dial it out. I would recommend trying out a fatter, warmer speaker like a cannabis rex if you want to really fatten up, loosen up and sweeten up a deluxe. Think of a fat jazzy, bluesy tone. If you prefer something, a bit tighter and less dark, try a texas heat. texas heats are in the jensen reissue vein but to me they just do everything better, thicker, warmer, smoother yet somehow still more articulate because you can turn up the treble without it spiking your ears. Great either clean or with overdrive. Last further option worth looking at is the maverick, so you can crank up your amp a little more, but control your volume at
the speaker. These are similar to texas heats, but perhaps more bright, again in the jensen vein, but again they do it better than jensens. Really useful in non master amps like deluxes.
Last thing you might want to look at after these is doing the "nashville mod" which is simply a resistor swap. Deluxes do not have a mid control pot like the bigger fenders, but they do have a resistor. At 4.7k ohms it is more or less the same as having your mids permanently set at 5 or 6. If you swap to a 10k resistor, it is the same as cranking them to 10. It wont make you amp more spiky, but it will make it sound a little thicker. You may even want to try a few values between 4.7 and 10k but most folks find that either they like the stock sound, or want more mids, in which case the 10k ohm resistor does the job.
